The effectiveness of the discharges in the working gap of a spark erosion plant and, consequently, the design of the spark generator play a decisive part in the economic operation of the spark erosion process. Previously, pulse generators have been used which provide a current limitation by the use of ballast resistors to protect the power supply against excessive current loads during a discharge in the working gap. The ballast resistors are also intended to protect the semiconductor switches. However, it was recognized that ballast resistors are prejudicial to the desirable power increase of the generator.
DE-OS No. 2,908,696 proposes providing a spark erosion generator without ballast resistors, in which the positive high frequency half-waves of the generator circuit are supplied to the spark gap with timed interruption. However, this approach leads to undesirably high-ripple discharge pulses with short interruptions of the power supply. The interruptions may be so short that all pulses lead to a discharge in the same discharge channel However, this condition makes control of the spark erosion installation less flexible rather than permitting a broad variation of the different process parameters.